Remove .flowconfig from hermes/inspector/tools/msggen

Summary:
Changelog: [Internal]

This separate `.flowconfig` file was causing versioning issues.
Delete it so that `msggen` can share the same flowconfig as the rest
of React Native.

Reviewed By: willholen

Differential Revision: D19413710

fbshipit-source-id: 748cb50a3151df1c67ee7176e57e259e48f50be7